This application claims priority of Japanese Application Nos. 2000-236877 filed Aug. 4, 2000 and 2000-236878 filed Aug. 4, 2000, the complete disclosure of which are hereby incorporated by reference.
The invention relates to a diaryl carbonate product containing little impurities and a process for production of polycarbonate from the diaryl carbonate product.
Diaryl carbonate is known as a starting compound for producing a variety of chemical compounds, particularly, polycarbonate. For the production of polycarbonate, a diaryl carbonate is reacted with a polyhydric aromatic compound such as a bisphenol compound under polycondensation reaction in the presence of a catalyst.
The polycarbonate has excellent property in mechanical strength, transparency, electric characteristics, and optical characteristics, and is widely employed, for instance, for producing substrate of compact discs and other electric and electronic materials, organic glassy materials, and optical lenses.
There are known various processes for preparing a diaryl carbonate such as transesterification of dialkyl carbonates and reaction of phosgene and a phenol compound.
Recently, a process for producing a diaryl carbonate by decarbonylation of a diaryl oxalate has been invented as is described in U.S. Pat. No. 5,648,510. Further, U.S. Pat. No. 5,892,091 teaches that the decarbonylation of a diaryl oxalate is favorably performed in the presence of such a catalyst as an organic phosphorus compound.
U.S. Pat. No. 5,922,827 describes a process for producing polycarbonate from a diaryl carbonate prepared by decarbonylation of a diaryl oxalate.
The present inventors have studied to employ the diaryl carbonate prepared by the decarbonylation of a diaryl oxalate for producing a polycarbonate by reacting it with a polyhydric compound. In the course of the study, the inventors have noted that the polycarbonate produced by the use of a diaryl carbonate prepared by the decarbonylation of a diaryl oxalate is likely colored to have a yellow color. The colored polycarbonate is disadvantageous particularly in the case that the polycarbonate is employed for producing optical elements such as optical discs and optical lenses.
Therefore, the inventors have studied further to find causes by which the polycarbonate is colored. As a result, they have discovered that a furan ring-containing compound is contained in the diaryl carbonate-containing reaction product obtained by the decarbonylation, and that the furan ring-containing compound colors the resulting polycarbonate yellow, even if the amount of the furan ring-containing compound is very small. A representative furan ring-containing compound is benzofuran-2,3-dione which is assumed to be produced by Fries rearrangement of the diaryl oxalate.
It is then confirmed that a less colored polycarbonate resin can be produced when a diaryl carbonate product of which furan ring-containing compound content is decreased to a level of less than 1 ppm (wt. ppm) is employed for the production of polycarbonate.
Accordingly, the present invention resides in a composition comprising a diaryl carbonate and a furan ring-containing compound in an amount of not more than 1 ppm (by weight). The composition of the invention is preferably derived from a reaction mixture of decarbonylation reaction of a diaryl oxalate.
A representative furan ring-containing compound is benzofuran-2,3-dione or its derivative which is assumed to have been derived from the diaryl oxalate via side-reaction.
The invention further resides in a process favorably employable for preparing the composition of the invention containing little amount of the by-produced furan ring-containing compound, which comprises the steps of:
recovering from the reaction mixture of decarbonylation, a first distillate comprising a diaryl carbonate, a furan ring-containing compound, an unreacted diaryl oxalate, and other by-products, by distillation (or evaporation);
recovering from the first distillate, a second distillate comprising a diaryl carbonate in an amount of not less than 95.0 wt. %, a furan ring-containing compound in an amount of 1 to 2,000 ppm, and an unreacted diaryl oxalate in an amount of not more than 1 wt. %, by distillation; and
removing from the second distillate at least a portion of the furan ring-containing compound.
The invention further resides in a process for preparing polycarbonate which comprises reacting a polyhydric compound with a composition of the invention comprising a major portion of a diaryl carbonate and a furan ring-containing compound in an amount of not more than 1 ppm.